Plastic scintillators are polymer-based detector materials for gamma radiation, fast neutrons and other charged particles. Scintillators generate a flash of light when ionizing radiation is absorbed (gamma, alpha, and/or neutron) (herein collectively “neutron”). Their low cost, fast-timing resolution and ease of large-scale production make it a first-line detection method compared to inorganic crystal scintillators. However, due to the absence of high neutron capture isotopes in plastic scintillators, they are unable to detect thermal neutrons and are therefore concurrently used with 3He gas detectors, for example, to detect illicit trafficking of special nuclear materials (SNM). Due to 3He scarcity and increasing demand, alternative isotopes such as 10B and 6Li with comparable thermal neutron capture cross sections and higher natural abundances have been investigated. Current developments of neutron sensitive plastic scintillators mainly rely on commercially available carboranes as a boron source due to their high boron content. Thermal neutrons are detected via the capture reaction on the nucleus of 10B and measuring the scintillation light produced by the alpha particles (4He) released by this reaction, shown in equation (1). Although carboranes have high boron content (˜75% wt.), they have limited solubility in plastic scintillator formulations, are very expensive, and the cost is significantly higher in their 10B enriched form.
                                                                                10                    ⁢          B          +          n                =                  {                                                                                                                                                                                    7                                        ⁢                    Li                                    ⁢                                      +                    4                                    ⁢                  He                                                                                                  Q                    =                                          2.792                      ⁢                                                                                          ⁢                      MeV                                                        ,                                      6                    ⁢                    %                                                                                                                                                                                                                                      7                                        ⁢                    Li                                    ⁢                                      +                    4                                    ⁢                  He                  +                                      Y                    (                                                                  480                        ⁢                                                                                                  ⁢                        keV                                            ,                                                                                                                                        Q                    =                                          2.310                      ⁢                                                                                          ⁢                      MeV                                                        ,                                      94                    ⁢                    %                                                                                                          (        1        )            
Alternative methods of thermal neutron detection include boron containing semiconductor crystals, enriched boron-10 fluoride (10BF3) gas filled proportional counters, and boron lined tube counters along with liquid scintillators doped with boron compounds such as trimethyl borate. However, growing crystals in large quantities for significant area coverage is difficult and 10BF3 has severe limitations in deployment due to its toxicity. While boron lined tubes are physically similar to 3He tubes, they suffer from reduced efficiencies due to the energy loss effects from having a solid boron wall coverage. Trimethyl borate mixed into liquid scintillators of many varieties has a very low flash point and is required to be very well sealed from oxygen in order to reduce quenching effects and maintain efficiency. Other isotopic candidates for scintillators such as 6Li or 155Gd/157Gd are not attractive due to higher cost, lack of availability, and reduced compatibility with inexpensive polymer matrices. Furthermore, the price of substitute matrices needs to be comparable to that of the polymers in order to achieve neutron sensitivity in a cost effective manner. Alternatives to carboranes need to be produced with efficient synthesis methods and inexpensive reagents.
With regard to boron containing organic materials, recently direct borylation of activated C—H bonds of aromatic compounds has been reported using iridium-based catalysis. However, high Ir catalyst loadings, lack of regioselectivity and longer reaction times hinder its applicability and scale up potential. In order to counter these disadvantages, the synthesis of 1,3,6,8 tetrakis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) pyrene was reported by Matsumoto and coworkers by nickel catalyzed direct borylation achieving a yield of 74% in two days (Matsumoto, A. et al. A kinetically protected pyrene: molecular design, bright blue emission in the crystalline state and aromaticity relocation in its dicationic species. Chem Commun 50, 10956-10958 (2014)). Furthermore, synthesis of 1,2,4,5-tetrakis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene was reported by Wagner and coworkers with an overall yield of 64%; however, their synthetic process was a two-step reaction system achieving only partial borylation and the use of highly pyrophoric and toxic reagents such as n-butyl lithium and Grignard reagents. Seven, O., et al., M. High-Yield Syntheses and Reactivity Studies of 1,2-Diborylated and 1,2,4,5-Tetraborylated Benzenes. Organometallics 33, 1291-1299 (2014). Both Aubert et al. (Geny, A. et al. Cobalt(I)-mediated preparation of polyborylated cyclohexadienes: Scope, limitations, and mechanistic insight. Chem-Eur J 13, 5408-5425 (2007)) and Gandon et al. (Iannazzo, L. et al., Alkynylboronates and -boramides in Co—I— and Rh—I Catalyzed [2+2+2] Cycloadditions: Construction of Oligoaryls through Selective Suzuki Couplings. Eur J Org Chem, 3283-3292 (2011). doi: 10.1002/ejoc.201100371) utilized cobalt-catalyzed [2+2+2] cycloaddition of ethynyl pinacol borate to yield a mixture of 2,2′,2″-(benzene-1,2,4-triyl)tris(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) and 1,3,5-tris(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene with a yield of 63%. Their use of an expensive borylating reagent (ethynyl pinacol borate—$650/g) and a difficult separation of the product mixture could be detrimental to using this reaction system. Compared to cobalt-catalyzed cycloaddition reactions, Wang et al. achieved 85% yield by direct borylation of 1,3,5-tribromobenzene using Miyuara conditions. Bao, B. et al., Water-Soluble Hyperbranched Polyelectrolytes with High Fluorescence Quantum Yield: Facile Synthesis and Selective Chemosensor for Hg2+ and Cu2+ Ions. J Polym Sci Pol Chem 48, 3431-3439 (2010); Liu, Y. W. et al, Synthesis and properties of starburst amorphous molecules: 1,3,5-tris(1,8-naphthalimide-4-yl)benzenes. Synth Met 160, 2055-2060 (2010).
The present invention addresses and overcomes these and other issues, and more specifically provides a cost effective composition and method of making a scintillator for neutron and gamma detection for use in a number of industrial applications.